linux-kernel - Re: [PATCH] arm64: dts: rockchip: Change ethernet TXD timing delay value

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Message-ID: <jwvseh3v8n5.fsf-monnier+@gnu.org>
Date: Wed, 03 Sep 2025 12:10:46 -0400
From: Stefan Monnier <monnier@....umontreal.ca>
To: Dongjin Kim <tobetter@...il.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: rockchip: Change ethernet TXD timing delay
 value

Dongjin Kim wrote:
> On Tue, Aug 19, 2025 at 06:03:47PM +0200, Andrew Lunn wrote:
> > On Tue, Aug 19, 2025 at 01:50:17PM +0900, Dongjin Kim wrote:
> > > Very poor network performance is observed on the ODROID-M1 Board
> > > (REV 1.0 20220613) when running iperf3 (under 200Mbits/sec), and
> > > this problem can be resolved after changing the value of TXD
> > > timing to 0x35 from 0x4f.
> > 
> > How did you decide on 0x35?
> > 
> > ~/linux/arch/arm64$ grep -hr "tx_delay = " | sort | uniq -c
> >       4 	tx_delay = <0x10>;
> >       1 	tx_delay = <0x1a>;
> >       1 	tx_delay = <0x21>;
> >       2 	tx_delay = <0x22>;
> >       4 	tx_delay = <0x24>;
> >       2 	tx_delay = <0x26>;
> >      14 	tx_delay = <0x28>;
> >       1 	tx_delay = <0x2a>;
> >       6 	tx_delay = <0x30>;
> >       1 	tx_delay = <0x3a>;
> >       3 	tx_delay = <0x3c>;
> >       2 	tx_delay = <0x42>;
> >       5 	tx_delay = <0x43>;
> >       2 	tx_delay = <0x44>;
> >       1 	tx_delay = <0x46>;
> >       6 	tx_delay = <0x4f>;
> > 
> > The numbers are all over the place, but it is clear that 0x28 is the
> > most popular for some reason. But since this delay values are magic,
> > i've no idea why.
> > 
> >      Andrew
> I do have more numbers in the Rockchip BSP kernel, and 0x35 is from
> one of them that shows less retry counts when testing 'iperf3' while
> testing with the batch of ODROID-M1. :)

FWIW, I had trouble with my Odroid-M1 whose outgoing ethernet bandwidth
seemed to be limited to an average around 100kB/s, when I bumped into
this thread.  I applied the patch and I can now download from that
Odroid at >80MB/s.  So:

    Tested-by: Stefan Monnier <monnier@....umontreal.ca>

Haven't tried the `rgmii-id` patch yet.


        Stefan